1. Field of the Invention
This invention relates to a printing system having a function of printing not only on ordinary sheets such as web sheet or cut sheets, but also on labels removably adhered to a backing web.
2. Description of Related Art
A typical printing system for printing on labels is disclosed, for example, in British unexamined patent publication No. 2,194,488A laid open of Mar. 9, 1988.
In such a printing system, a separating roller which bends and guides a backing wet contacting with a side on which labels are not adhered is arranged in a downstream side of a platen in a paper feeding direction, and a paper holding roller is arranged between the platen and the separating roller.
The paper holding roller is biased toward the outer periphery of the platen and moves between a holding position contacting with the outer periphery of the platen and releasing position separating therefrom by a predetermined distance.
The backing web with labels extends to a pull tractor through the platen, the paper holding roller, and the separating roller, and the labels adhered on the backing web are printed on the platen. The backing web with printed labels is fed in the feeding direction by the tractor. In this moment, the tension force in the feeding direction of the backing web acts on the backing web with the printed labels. The paper holding roller is moved in a direction away from the platen by the tension force resulting from the above feeding movement, against its normal bias in the direction of the platen.
Further, the position of the paper holding roller is not fixed because the tension force which acts on the backing web changes according to the change of the feeding speed of the backing web. Specifically, the paper holding roller moves to a tangent common to the platen and the separating roller when the feeding speed of the backing web becomes fast and the tension which acts on the backing web becomes great.
In the printing system of the construction described above, the label is not always separated from the backing web by the separating roller, and is fed with the backing web being curved along the separating roller.